A composite film of an acrylic polymer and a urethane polymer is known as a film capable of satisfying both high strength and high breaking elongation and is disclosed, for example, in JP-A-2003-96140, JP-A-2003-171411, JP-A-2004-10661 and JP-A-2004-10662. These composite films have tough physical properties as a film, such as high strength and high breaking elongation, but in use, for example, as a base material of a pressure-sensitive adhesive for protecting the automotive painted surface or the like, the flexibility of the film is disadvantageously insufficient. Particularly, when working in a low-temperature state, for example, working of laminating a pressure-sensitive adhesive sheet to an adherend in cold regions, is performed, the film cannot follow the unevenness of the adherend surface due to insufficient flexibility of the base material and is sometimes separated or lifted.